1. Field of the Invention
The present invention relates to a piping joint, and more particularly to an ultrafine finish piping joint for use in piping, etc., leading to a clean room which requires cleanness.
2. Description of the Prior Art
In the semiconductor field, ICs and LSIs are treated in general in a clean room with fine particles and dust, etc., completely removed therefrom. Thus the treatment must be effected under very severe manufacturing environments and conditions. Such semiconductor manufacture needs specialty gas which is introduced from the outside of the clean room through piping. Accordingly, the manufacture dislikes to an extreme foreign gases such as air and the like mixed with the specialty gas, and requires ultrafine finish for the piping as well as for piping joints serving to connect the pipes with each other.
Hereupon, a prior piping joint of this type has a seal packing disposed between a couple of joint pieces, wherein a box nut is threaded into one of the joint pieces from the other thereof for clamping both joint pieces. In this case, the piping joint suffers from some drawbacks in that upon clamping the box nut by the rotation thereof the other joint piece is rotated together with the box nut so as to cause not only the seal packing to be twisted with a fear of the seal packing being broken but also to cause piping connected with the other joint piece to be twisted with a fear of damaging the piping itself. Hereupon, a metal C ring is often used for rendering help to the sealing. However, the metal C ring is deformed owing to the twisting and sharply deteriorated in its sealing property.
To solve such a problem, a structure is considered wherein the end surface of the other joint piece described above is adapted to support many balls which balls are then brought into contact with the internal end surface of the box nut to prevent the other joint piece from being twisted. However, both the other joint piece and the box nut have flat surfaces by which the balls are supported. Accordingly, the balls bite into these flat surfaces upon tightening them and form grooves therein or cause portions of the flat surfaces corresponding to the respective balls to be unevenly depressed. Thus, they can not exhibit proper torque for tightening, with a fear that the C ring might be twisted.
Furthermore, in piping and joints for use in a clean room, etc., in a semiconductor field, specialty gas flowing through the piping must be frequently exchanged. In this case, rough inner surfaces of the piping or an improper sealing structure of the joint not only makes a fluid path resistive but also causes gas molecules previously employed to reside on uneven portions of the surfaces of the piping or to go round the back side of the sealing portion of the joint. This old gas exudes out of the sealing portion and mixes in exchanged, newly introduced gas. This badly affects semiconductor products.
Thus, such a prior piping joint is improper for use in piping to a clean room.
Hereupon, the inventors conducted experimental work to assure proper sealing between both joint pieces, wherein instead of the use of the other joint piece for supporting the balls a thrust bearing comprising high hardness materials such as stainless steel was simply interposed between the other joint piece and the box nut to prevent the flat surface of the box nut from being deformed. However, the simple interposition of the thrust bearing did not necessarily enable the metal C ring to be tightened in place. The reason is not clear at present. It may be however inferred that rings and balls, etc., being members of the thrust bearing are slightly displaced or inclined upon tightening the box nut, and thereby torsional stress is produced between the other joint piece and the box nut, and thus some torsion is also provided between the joint pieces to permit the the metal C ring to be abnormally deformed.
Accordingly, a piping joint capable of properly tightening the boxnut while making the most of the sealing property of the metal C ring is desired.